GE Multilin B30 Bus Differential System 5-655 SETTINGS 5.2 PRODUCT SETUP5The operand shall be configured to drive an output contact, user-programmable LED, or selected communication-basedoutput. Latching and acknowledging conditions - if required - should be programmed accordingly.The CRC alarm function is available on a per-channel basis. The total number of direct input and output messages thatfailed the CRC check is available as the ACTUAL VALUES STATUS DIRECT INPUTS CRC FAIL COUNT CH1 actualvalue.• Message count and length of the monitoring window: To monitor communications integrity, the relay sends 1 messageper second (at 64 kbps) or 2 messages per second (128 kbps) even if there is no change in the direct outputs. Forexample, setting the CRC ALARM CH1 MESSAGE COUNT to “10000”, corresponds a time window of about 160 minutes at64 kbps and 80 minutes at 128 kbps. If the messages are sent faster as a result of direct outputs activity, the monitor-ing time interval will shorten. This should be taken into account when determining the CRC ALARM CH1 MESSAGE COUNTsetting. For example, if the requirement is a maximum monitoring time interval of 10 minutes at 64 kbps, then the CRCALARM CH1 MESSAGE COUNT should be set to 10 × 60 × 1 = 600.• Correlation of failed CRC and bit error rate (BER): The CRC check may fail if one or more bits in a packet are cor-rupted. Therefore, an exact correlation between the CRC fail rate and the BER is not possible. Under certain assump-tions an approximation can be made as follows. A direct input and output packet containing 20 bytes results in 160 bitsof data being sent and therefore, a transmission of 63 packets is equivalent to 10,000 bits. A BER of 10–4 implies 1 biterror for every 10000 bits sent or received. Assuming the best case of only 1 bit error in a failed packet, having 1 failedpacket for every 63 received is about equal to a BER of 10 –4 .c) UNRETURNED MESSAGES ALARM CH1(2)PATH: SETTINGS PRODUCT SETUP DIRECT I/O UNRETURNED MESSAGES ALARM CH1(2)The B30 checks integrity of the direct input and output communication ring by counting unreturned messages. In the ringconfiguration, all messages originating at a given device should return within a pre-defined period of time. The unreturnedmessages alarm function is available for monitoring the integrity of the communication ring by tracking the rate of unre-turned messages. This function counts all the outgoing messages and a separate counter adds the messages have failedto return. When the unreturned messages counter reaches the user-definable level specified by the UNRET MSGS ALARMCH1 THRESHOLD setting and within the user-defined message count UNRET MSGS ALARM CH1 COUNT, the DIR IO CH1 UNRETALM FlexLogic™ operand is set.When the total message counter reaches the user-defined maximum specified by the UNRET MSGS ALARM CH1 MESSAGECOUNT setting, both the counters reset and the monitoring process is restarted.The operand shall be configured to drive an output contact, user-programmable LED, or selected communication-basedoutput. Latching and acknowledging conditions, if required, should be programmed accordingly.The unreturned messages alarm function is available on a per-channel basis and is active only in the ring configuration.The total number of unreturned input and output messages is available as the ACTUAL VALUES STATUS DIRECTINPUTS UNRETURNED MSG COUNT CH1 actual value. UNRETURNED MESSAGES ALARM CH1UNRET MSGS ALARM CH1FUNCTION: DisabledRange: Enabled, DisabledMESSAGE UNRET MSGS ALARM CH1MESSAGE COUNT: 600Range: 100 to 10000 in steps of 1MESSAGE UNRET MSGS ALARM CH1THRESHOLD: 10Range: 1 to 1000 in steps of 1MESSAGE UNRET MSGS ALARM CH1EVENTS: DisabledRange: Enabled, Disabled
